Stereodynamical control of cold HD + D2 collisions.

We report full-dimensional quantum calculations of stereodynamic control of HD(v = 1, j = 2) + D2 collisions that has been probed experimentally by Perreault et al. using the Stark-induced adiabatic Raman passage (SARP) technique. Computations were performed on two highly accurate full-dimensional H4 potential energy surfaces. It is found that for both potential surfaces, rotational quenching of HD from with concurrent rotational excitation of D2 from is the dominant transition with cross sections four times larger than that of elastically scattered D2 for the same quenching transition in HD. This process was not considered in the original analysis of the SARP experiments that probed ΔjHD = -2 transitions in HD(vHD = 1, jHD = 2) + D2 collisions. Cross sections are characterized by an l = 3 resonance for ortho-D2(jD2 = 0) collisions, while both l = 1 and l = 3 resonances are observed for the para-D2(jD2 = 1) partner. While our results are in excellent agreement with prior measurements of elastic and inelastic differential cross sections, the agreement is less satisfactory with the SARP experiments, in particular for the transition for which the theoretical calculations indicate that D2 rotational excitation channel is the dominant inelastic process.

Mixed quantum/classical theory (MQCT) approach to the dynamics of molecule-molecule collisions in complex systems.

We developed a general theoretical approach and a user-ready computer code that permit study of the dynamics of collisional energy transfer and ro-vibrational energy exchange in complex molecule-molecule collisions. The method is a mixture of classical and quantum mechanics. The internal ro-vibrational motion of collision partners is treated quantum mechanically using a time-dependent Schrödinger equation that captures many quantum phenomena including state quantization and zero-point energy, propensity and selection rules for state-to-state transitions, quantum symmetry and interference phenomena. A significant numerical speed up is obtained by describing the translational motion of collision partners classically, using the Ehrenfest mean-field trajectory approach. Within this framework a family of approximate methods for collision dynamics is developed. Several benchmark studies for diatomic and triatomic molecules, such as H2O and ND3 collided with He, H2 and D2, show that the results of MQCT are in good agreement with full-quantum calculations in a broad range of energies, especially at high collision energies where they become nearly identical to the full quantum results. Numerical efficiency of the method and massive parallelism of the MQCT code permit us to embrace some of the most complicated collisional systems ever studied, such as C6H6 + He, CH3COOH + He and H2O + H2O. Application of MQCT to the collisions of chiral molecules such as CH3CHCH2O + He, and to molecule-surface collisions is also possible and will be pursued in the future.

Novel Octahedral Nickel†(II) Complex with Flexible Piperazinyl Moiety Exhibits Potent Cytotoxic Effect Along with Anti-Migratory and Anti-Metastatic Effect on Human Cancer Cells.

Synthesis of non-platinum transition metal complexes with N,O donor chelating ligand for application against pathogenesis of cancer with higher efficacy and selectivity is currently an important field of research. We assessed the anti-cancer effect of a mixed ligand Ni(II) complex on human breast and lung cancer cell lines in this investigation. Mononuclear mixed ligand octahedral Ni(II) complex [NiIIL(NO3)(MeOH)] complex (1), with tri-dentate phenol-based ligand 2,4-dichloro-6-((4-methylpiperazin-1-yl) methyl) phenol (HL) along with methanol and nitrate as ancillary ligand was prepared. Piperazine moiety of the ligand exists as boat conformation in this complex as revealed from single crystal X-ray study. UV-visible spectrum of complex (1) exhibits three distinct d-d bands due to spin-allowed 3 A2 g→3T1 g (P), 3 A2 g→3T1 g(F) and 3 A2 g→3T2 g(F) transitions as expected in an octahedral d8 system. Our study revealed that Complex (1) induces apoptotic cell death in mouse and human cancer cells such as mcf-7, A549 and MDA-MB-231 through transactivation of p53 and its pro-apoptotic downstream targets in a dose dependent manner. Furthermore, complex (1) was able to slow the migratory rate of MDA-MB-231 cells' in vitro as well as epithelia -mesenchymal transition (EMT), the key step for metastatic transition and malignancy. Over all our results suggest complex (1) as a potential agent in anti-tumor treatment regimen showing both cytotoxic and anti-metastatic activity against malignant neoplasia.

Mixed quantum/classical calculations of rotationally inelastic scattering in the CO + CO system: a comparison with fully quantum results.

An updated version of the CO + CO potential energy surface from [R. Dawes, X. G. Wang and T. Carrington, J. Phys. Chem. A 2013, 117, 7612] is presented, that incorporates an improved treatment of the asymptotic behavior. It is found that this new surface is only slightly different from the other popular PES available for this system in the literature [G. W. M. Vissers, P. E. S. Wormer and A. Van Der Avoird, Phys. Chem. Chem. Phys. 2003, 5, 4767]. The differences are quantified by expanding both surfaces over a set of analytic functions and comparing the behavior of expansion coefficients along the molecule-molecule distance R. It is shown that all expansion coefficients behave similarly, except in the very high energy range at small R where the PES is repulsive. That difference has no effect on low collision-energy dynamics, which is explored via inelastic scattering calculations carried out using the MQCT program which implements the mixed quantum/classical theory for molecular energy exchange processes. The validity of MQCT predictions of state-to-state transition cross sections for CO + CO is also tested by comparison against full-quantum coupled-states calculations. In all cases MQCT gives reliable results, except at very low collision energy where the full-quantum calculations predict strong oscillations of state-to-state transition cross sections due to resonances. For strong transitions with large cross sections, the results of MQCT are reliable, especially at higher collision energy. For weaker transitions, and lower collision energies, the cross sections predicted by MQCT may be up to a factor of 2-3 different from those obtained by full-quantum calculations.

Mixed quantum/classical theory for rotational energy exchange in symmetric-top-rotor + linear-rotor collisions and a case study of the ND3 + D2 system.

The extension of mixed quantum/classical theory (MQCT) to describe collisional energy transfer is developed for a symmetric-top-rotor + linear-rotor system and is applied to ND3 + D2. State-to-state transition cross sections are computed in a broad energy range for all possible processes: when both ND3 and D2 molecules are excited or both are quenched, when one is excited while the other is quenched and vice versa, when the ND3 state changes its parity while D2 is excited or quenched, and when ND3 is excited or quenched while D2 remains in the same state, ground or excited. In all these processes the results of MQCT are found to approximately satisfy the principle of microscopic reversibility. For a set of sixteen state-to-state transitions available from the literature for a collision energy of 800 cm-1 the values of cross sections predicted by MQCT are within 8% of accurate full-quantum results. A useful time-dependent insight is obtained by monitoring the evolution of state populations along MQCT trajectories. It is shown that, if before the collision, D2 is in its ground state, the excitation of ND3 rotational states proceeds through a two-step mechanism in which the kinetic energy of molecule-molecule collision is first used to excite D2 and only then is transferred to the excited rotational states of ND3. It is found that both potential coupling and Coriolis coupling play important roles in ND3 + D2 collisions.

Description of quantum interference using mixed quantum/classical theory of inelastic scattering.

Manifestation of the quantum interference effect in the oscillation of scattering cross section is explored using the N2 + O system as a case study. Calculations are carried out for two electronic PESs of the system, for various initial rotational states of N2, in a broad range of N2 + O collision energies and using three theoretical methods: two versions of the approximate mixed quantum/classical theory (MQCT and AT-MQCT) and the accurate full-quantum coupled-channel method (implemented in MOLSCAT). A good agreement between different methods is observed, especially at high energies. Elastic scattering cross-sections oscillate as a function of collision energy, which is the result of quantum interference. The effects of initial rotational excitation and of the PES properties are studied in detail. For the final (thermally averaged) cross sections, both MOLSCAT and MQCT calculations predict a rather regular pattern of quantum oscillations that persist through a broad range of collision energies and expand into the low-energy regime where quantum scattering resonances are common. The difference between cross sections predicted by MQCT and MOLSCAT decreases from ∼8% at low energies to ∼2% at high energies. Experimental data available at high collision energies are well reproduced.

Adiabatic Trajectory Approximation: A New General Method in the Toolbox of Mixed Quantum/Classical Theory for Collisional Energy Transfer.

A new version of the MQCT program is presented, which includes an important addition, adiabatic trajectory approximation (AT-MQCT), in which the equations of motion for the classical and quantum parts of the system are decoupled. This method is much faster, which permits calculations for larger molecular systems and at higher collision energies than was possible before. AT-MQCT is general and can be applied to any molecule + molecule inelastic scattering problem. A benchmark study is presented for H2O + H2O rotational energy transfer, an important asymmetric-top rotor + asymmetric-top rotor collision process, a very difficult problem unamenable to the treatment by other codes that exist in the community. Our results indicate that AT-MQCT represents a reliable computational tool for prediction of collisional energy transfer between the individual rotational states of two molecules, and this is valid for all combinations of state symmetries (such as para and ortho states of each collision partner).

Adiabatic Trajectory Approximation within the Framework of Mixed Quantum/Classical Theory.

A hierarchy of approximate methods is proposed for solving the equations of motion within a framework of the mixed quantum/classical theory (MQCT) of inelastic molecular collisions. Of particular interest is a limiting case: the method in which the classical-like equations of motion for the translational degrees of freedom (scattering) are decoupled from the quantum-like equations for time evolution of the internal molecular states (rotational and vibrational). In practice, trajectories are pre-computed during the first step of calculations with driving forces determined solely by the potential energy surface of the entrance channel, which is an adiabatic trajectory approximation. Quantum state-to-state transition probabilities are computed in the second step of calculations with an expanded basis and very efficient step-size adjustment. Application of this method to H2O + H2 rotationally inelastic scattering shows a significant computational speedup by 2 orders of magnitude. The results of this approximate propagation scheme are still rather accurate, as demonstrated by benchmarking against more rigorous calculations in which the quantum and classical equations of motion are held coupled and against the full-quantum coupled-channel calculations from the literature. It is concluded that the AT-MQCT method (the adiabatic trajectory version of MQCT) represents a promising tool for the computational treatment of molecular collisions and energy exchange.

Calculations of Differential Cross Sections Using Mixed Quantum/Classical Theory of Inelastic Scattering.

It is shown that the mixed quantum/classical theory (MQCT) for the description of molecular scattering is considerably improved by using integer values of orbital angular momentum l, just like in quantum theory, instead of treating it as a continuous classical variable related to the impact parameter. This conclusion is justified by the excellent accuracy of the modified theory for prediction of the differential cross sections, at various values of collision energy and in both forward and backward scattering regimes. This approach requires fewer trajectories, compared to the random Monte Carlo sampling, and the only convergence parameter is lmax (maximum orbital angular momentum) similar to Jmax in the full quantum theory (maximum total angular momentum). Calculations of differential and integral cross sections for elastic and inelastic channels are presented, and the role of the scattering phase is discussed. The low-energy range is analyzed in detail to obtain insight into how the mixed quantum/classical treatment works in the scattering regime dominated by resonances. The differential cross section for rotationally inelastic scattering, computed by MQCT approach, is presented for the first time.

Molecular dynamics approach to understand the denaturing effect of a millimolar concentration of dodine on a λ-repressor and counteraction by trehalose.

Commonly used denaturants for protein denaturation are conventionally required in high concentrations in order to produce their effects. In this study, a molecular dynamics simulation of a mutated version of the N-terminal domain of a λ-repressor is carried out in the presence of a 10 millimolar (mM) concentration of dodine. Such a small concentration is found to be effective for denaturation of the protein. Both electrostatic and van der Waals interactions (between protein and dodine) play a role in the denaturation process and we observe more denaturation at the terminal helices. Three different molar concentrations of trehalose are used in order to check the counteraction against the action of dodine. This study shows that 0.5 and 1.0 M trehalose are sufficient to counteract the action of dodine. The study also sheds light on the fact that some protein sites are more responsive to unfolding, which is evident from the helical fractions of the terminal helices for different systems. The counteraction of trehalose on dodine-induced protein denaturation is found to be due to the replacement of some of the dodine molecules by trehalose molecules in the solvation shell of the protein. Preferential solvation of dodine molecules by trehalose molecules through hydrogen bonding interactions also plays a vital role in stabilizing the native conformation of the protein in a high trehalose concentration. Replacement of protein-dodine and protein-water hydrogen bonds by protein-trehalose hydrogen bonds is also observed.